1. Field of the Invention
The invention relates to analog voltage comparators and means for selectively controlling the output of the comparator responsive to the input voltages.
2. Description of the Related Art
Comparators are well-known analog electronic devices having a variety of applications. Generally, a comparator has only two logic state outputs, each state reflecting the relative amplitudes of two analog input variables. The analog input variables are typically termed reference input (or inverting input) and test input (or non-inverting input). Usually, the comparator outputs a logic level HIGH state when the amplitude of the inverting input variable is less than the amplitude of the non-inverting input variable. Conversely, the typical comparator outputs a logic level LOW state when the inverting input variable is greater than the noninverting input variable.
A typical comparator may comprise an amplifier specifically designed for null comparison measurement. In many practical applications, the reference and test input variables to a comparator are subject to signal disruptions such as noise or oscillation. These signal disruptions can cause unwanted state changes in the logic state output of a comparator. A Schmitt-trigger is a well-known analog circuit which also includes a two-state logic output, and is often utilized to overcome input signal noise since Schmitt-triggers have different switching thresholds, depending on whether the input is changing from LOW to HIGH or from HIGH to LOW. The difference between the switching thresholds is generally termed hysteresis.
The programmable voltage comparator of the present invention utilizes hysteresis to reduce the effect of these small oscillatory changes of the comparator's input variables on the comparator's output.
As noted above, differential amplifiers are ideally suited for providing the comparator function in solid-state circuitry. Various circuit techniques are well known in the art for providing feedback from the output of a comparator to adjust the switching states of the comparator's output responsive to the input variables. However, to the best of Applicant's knowledge, no such circuit technique exists for providing a programmable means for adjusting the input voltage required to initiate a switching of the output state of the comparator.